1. Field of the Invention
The present invention relates to glucoamylase variants, polynucleotides encoding the variants, methods of producing the variants, and methods of using the variants.
2. Description of the Related Art
Glucoamylase (1,4-alpha-D-glucan glucohydrolase, EC 3.2.1.3) is an enzyme, which catalyzes the release of D-glucose from the non-reducing ends of starch or related oligo- and polysaccharide molecules. Glucoamylases are produced by several filamentous fungi and yeast, with those from Aspergillus being commercially most important.
Commercially, glucoamylases are used to convert starchy material, which is already partially hydrolyzed by an alpha-amylase, to glucose. The glucose may then be converted directly or indirectly into a fermentation product using a fermenting organism. Examples of commercial fermentation products include alcohols (e.g., ethanol, methanol, butanol, 1,3-propanediol); organic acids (e.g., citric acid, acetic acid, itaconic acid, lactic acid, gluconic acid, gluconate, lactic acid, succinic acid, 2,5-diketo-D-gluconic acid); ketones (e.g., acetone); amino acids (e.g., glutamic acid); gases (e.g., H2 and CO2), and more complex compounds, including, for example, antibiotics (e.g., penicillin and tetracycline); enzymes; vitamins (e.g., riboflavin, B12, beta-carotene); hormones, and other compounds which are difficult to produce synthetically. Fermentation processes are also commonly used in the consumable alcohol (e.g., beer and wine), dairy (e.g., in the production of yogurt and cheese) industries.
The end product may also be syrup. For instance, the end product may be glucose, but may also be converted, e.g., by glucose isomerase to fructose or a mixture composed almost equally of glucose and fructose. This mixture, or a mixture further enriched with fructose, is the most commonly used high fructose corn syrup (HFCS) commercialized throughout the world.
It is an object of the present invention to provide polypeptides having glucoamylase activity and polynucleotides encoding the polypeptides and which provide a high yield in fermentation product production processes, such as ethanol production processes, including one-step ethanol fermentation processes from un-gelatinized raw (or uncooked) starch. Copending patent application, WO2011/127802, discloses a wild type glucoamylase from Penicillium oxalicum. 
The present invention provides a glucoamylase variant with improved properties compared to its parent.